The present invention relates to a power supply apparatus.
The output power of a fuel cell varies mainly depending on the variation in fuel feeding rate. The output power of a solar cell varies mainly depending on the variation in amount of solar radiation. Conventionally, in such a power supply apparatus having a power generating device (cell), the output power of which supplied to a load varies according to the power generating condition, DC output power of the power generating device has been converted into a power of a constant voltage or a constant current by using a DC-DC converter or a DC-AC converter to output it.
A prior art fuel cell apparatus is disclosed in Japanese Patent Laid-Open Publication No. 2000173636. In the prior art fuel cell apparatus, the DC power generated in the fuel cell main body itself is converted into a DC power of a specified voltage by using a DC-DC converter and the converted DC power is constantly supplied to output terminals connected to an external load.
A prior art electric power storage apparatus for a solar cell is disclosed in Japanese Patent Laid-Open Publication No. 7-336910. In the prior art electric power storage apparatus for a solar cell, a generated voltage of the solar cell is transformed and the output power is stored in a storage battery. A transformation means is controlled so as to maximize a charging current of the storage battery (output current of the transformation means).
The fuel cell has a characteristic that the response of the variation in the output power depending on the variation in the fuel feeding rate is slow. In the prior art fuel cell, it is necessary to constantly supply the fuel exceeding considerably the amount required to the fuel cell so as respond quickly to the event of rapid increase in load. This decreases the usage efficiency of the fuel cell. Further, in the case of a fuel cell that uses methanol as fuel, a considerable amount of unused-methanol is discharged. This raises the problem on the purification method of the discharged methanol. In the prior art fuel cell, the operation of constantly controlling the discharge rate of methanol below a predetermined value cannot be performed.
On the other hand, in the case of using the prior art electric power storage apparatus for a solar cell by connecting to an external load, due to change in temperature of a solar cell panel or load side power, the apparatus can be used under the condition outside the maximum efficiency of the solar cell.
Conventionally, in the power generating device in which the output power supplied to the load varies depending on the power generating condition, it has been a problem in this field to provide a power supply apparatus that is constantly operable under a desired operating condition (for example, an operating condition under which amount of the fuel discharged from the fuel cell becomes minimum or the output power of the solar cell becomes maximum).
The present invention is to solve the above-mentioned conventional problem, and in a power supply apparatus having a power generating device in which the output power supplied to the load varies depending on the power generating condition, and it intends to provide a multi-purpose power supply apparatus that is constantly operable under a desired operating condition even if the power generating condition changes.